NITROGEN-REJECTING MEMBRANES TO INCREASE GAS HEATING VALUE: A SIMPLE WELLHEAD APPROACH

摘要

The Gas Research Institute (GRI) has estimated that approximately 17% of the natural gas reserves in the United States cannot be used because of high nitrogen content. Typical nitrogen-rich gas can occur naturally or come from well works that contain 5-50 mol% nitrogen. Sometimes, it can be tail end gas from a gas processing facility, containing as much as 60 mol% nitrogen. This high nitrogen content gas with low heating value cannot be used as fuel or put directly into a pipeline. Significant amounts of nitrogen—rich gases that cannot be piped need to be flared. This represents an environmental issue as well as a significant production loss.At present, the only proven technology available to upgrade this gas to pipeline specification is cryogenic separation. However, cryogenic plants are complex, require numerous moving parts and have high capital and operating costs. Furthermore, cryogenic plants must process a relatively high volume of gas, typically in the range of 50 to 500 million standard cubic feet per day, before they are economical. As a result, remote fields and some smaller gas fields cannot be treated economically.Membrane Technology and Research, Inc. (MTR) has a proven NitroSep™ membrane-based separation process to remove excess nitrogen from natural gas. Skid-mounted compact membrane units make this process very suitable for remote wellheads, for small fields with shorter production life and also for the wellhead processing of gas produced during venting after a well work-up.This paper describes membrane applications for nitrogen removal and processes used, provides data from laboratory and field tests, and discusses two commercial installations as case studies.